Introduction: The Richard M. Lucas Magnetic Resonance and Spectroscopy Imaging Center (Center) was awarded a five year NIH P41 Research Resource grant effective January 1, 1995. The Center forms a nucleus of scientific support for collaborations in medical imaging and MR spectroscopy research for researchers throughout the United States. No other research facility on the West Coast offers the unique resources provided by the Center. SRI is a well-established, local research facility which was awarded an NIH grant to study brain morphology in twins. To carry out this research project, SRI requires medical imaging facilities and equipment such as those available at the Center. The NHLBI Twin Study is the largest cardiovascular study of twins in the world and has produced over 200 scientific publications. Dr. Carmelli is considered an expert in genetic study of twins and this study, involving collaboration of four academic institutions, will be the first to determine the contribution of genetic and environmental factors to brain morphology. Discussion: SRI will perform magnetic resonance imaging scans on 80 sets of twins. These are male World War II veteran twins who have been involved in a longitudinal study of cardiovascular disease since 1969. The purpose of this fourth follow-up exam is to determine the relationship between cardiovascular risk factors collected over 23 years of follow-up, changes in cognitive function since the last exam, and brain morphology assessed by magnetic resonance imaging. This study provides an unprecedented opportunity to examine previously unexplored associations between CVD risk factors and indices of brain aging in older twins.